Many electronic devices and systems have the capability to store and retrieve information in a memory structure. In the von Neumann architecture which is typically used in modern electronic devices information is processed in a central processing unit (CPU) while information is stored in a separate memory. Thus the information has to be transmitted between CPU and memory for processing and storing. Schematically this is depicted in FIG. 1a for an integrated circuit 20 where data is transferred between a CPU and separate memories (SRAM and eNVM). For high speed processing, such information transfer represents a bottleneck called the “von Neumann bottleneck”, which has a negative impact on processing speeds of devices. The temporary storage of information and the random accessing of information become more important as storage technologies interface more directly with the processor of an electronic system. To reduce the effort in terms of power consumption and information transmission time, there is a need for innovative combinations of new devices and architectures which could extend the current CMOS technology by providing new information processing platforms. “Logic in Memory” (LiM) and neuromorphic circuits address the von-Neumann architecture bottleneck by reducing the transit times of information due to the use of the non-volatile memory (NVM) elements for information processing and fine-grained implementation of logic circuits directly with memory elements in the processing unit. A number of different non-volatile memory devices have been demonstrated in such concepts, including Flash, resistive RAMs (ReRAM), magnetoresistive RAM (MRAM), and phase change memory (PCM).
With regard to ferroelectric (FE) structures, non-volatile memory (NVM) elements can be realized as capacitor type (e.g., a FeRAM) or transistor type (FeFET) solutions, where information can be stored as a certain polarization state of a ferroelectric material layer within the structure. The ferroelectric material used is hafnium dioxide (HfO2) or zirconium dioxide or a solid solution of both transition metal oxides. In the case of pure hafnium oxide, the remnant polarization can be improved by adding a dopant species incorporated into the HfO2 layer during the deposition.
The ferroelectric material is intended to partially or fully replace the gate oxide of a transistor or the dielectric of a capacitor. Switching is caused by applying an electrical field via a voltage between the transistor gate and transistor channel. Specially, for n-channel transistors, ferroelectric switching after applying a sufficiently high positive voltage pulse causes a shift of the threshold voltage to lower or negative threshold voltage values. For p-channel transistors a negative voltage pulse causes a shift of the threshold voltage to more positive threshold voltage values.
FeFET memory devices have advantages over other types of non-volatile storage devices. Generally FeFET memory devices offer faster sensing and programming access times and lower power consumption during programming operation due to the specific physical storage mechanism. Further, FeFET memory devices are easier to integrate into High-k metal gate CMOS technology since the materials employed for FeFET memory devices are already used as gate oxide or DRAM dielectric materials. These advantages, and others, may explain the increasing popularity of FeFET memories for embedded storage as well as for stand-alone applications to be adopted in devices such as memory cards, USB flash drives, mobile phones, digital cameras, mass storage devices, MP3 players and the like.